System.Web.Mail.MailMessage - Conversation Type and NTLM auth

[Raj]

I have 2 question regarding System.Web.Mail.MailMessage and System.Net.Mail
1. In outlook we can arrange our emails based on Conversation.
How can we set this property in the emails which we send through the above
mentioned classes.

2. Currently I am using authentication type as NTLM, i.e.
"http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", "2"
Since the System.Web.Mail is obsolete, can we have similar property in
System.Net.Mail

Thanks,
Raj